Bingying Pan

Abstract The S  = 1/2 Heisenberg antiferromagnetic chain is a paradigmatic quantum system hosting exotic excitations. Using nuclear magnetic resonance (NMR) on copper benzoate, we characterise three distinct types of excitations by tuning the magnetic field at ultra-low temperatures. At 0.2 T, a nearly constant spin-lattice relaxation rate (1/T1) and a divergence-like spin-spin relaxation rate (1/T2G) upon cooling provide experimental evidence for spinon excitations.

Realization of a perfect two-dimensional Heisenberg ferromagnetic system: synthesis, structure and thermodynamic properties of PTBC Bingying Pan, Jiaxi Qiu, Binglin Pan, Xiangnan Gong, Shiyan Li, Yuliang Xu, Xiangmu Kong, Mingcui Ding, Lichun Zhang  and Hu Feng Abstract As the prototype of the Mermin-Wagner theorem, two-dimensional Heisenberg ferromagnets (2D HFM) should have no static order at finite temperatures [N. D. Mermin and H. Wagner et al., Phys. Rev. Lett., 1966, 17, 1133].

Figure 1 shows the constant-energy images of spin fluctuations in the (H, K) plane. Here, in the high-temperature tetragonal phase (110 K), the spin response is strongest at Q=(1, 0) (marked by dashed ellipse) at 15 meV (Fig. 1b), which is consistent with previous low-energy measurements12, 13. With an increase in energy (Fig. 1c–j), the spin fluctuations show anisotropic dispersion and counter-propagate mainly along the K direction.